Often the best photos of people interacting, particularly parents with children, are the ones where neither of the participants knows they are being photographed.

With no thought of the camera to inhibit their activities (or stifle their affections in the case of older kids), pictures taken of kids and parents spending time together reveal sweet and poignant moments. Capturing these brief interludes requires a bit of journalistic finesse on your part, but the results add great emotional depth to the family album.

The activity that your subjects are involved in doesn’t have to be profound or even obviously emotional. Often the most tender or touching moments arise out of everyday incidents: Siblings sharing a tender moment, a parent and child cuddling in a chair, or a couple just casually enjoying a walk together.

When you find your subjects involved in some natural and meaningful activity, seek a position that puts a plain background behind them. The simpler the activity, and the less movement, the better, generally (though certainly a mom pushing the kids on a swing works better as an action photo) because it lets you concentrate more on the relationship between the subjects.

A medium telephoto lens or zoom setting is ideal for photographing candidly because it lets you move to a discrete distance and still keep your subjects large in the frame.

How close you can work really depends on how sensitive your subjects are, but generally it’s worth sacrificing close-up facial expressions to remain at a friendly working distance. The longer you go unnoticed, the more photo opportunities you’ll get; and once you get a few distant shots you might want to tighten up the circle and edge your way closer to your subjects.

Be patient and wait for that one “decisive moment,” as Henri Cartier-Bresson described it, to record that instant that defines the relationship between your subjects.

It’s a wonderful thing when you watch an event unfolding through a viewfinder and an instantaneous moment of wonder happens: a butterfly briefly landing on your daughter’s hand as she sits in the garden with her father.

One interesting point about photographing parents and kids together is that, while it’s nice from a personal standpoint if the subjects are members of your family, from a photographic point of view, the pictures work even if they are of strangers.

If you happen to see a particularly interesting or cute moment in the park between a dad and his daughter, for instance, give your journalistic skills some practice and try to capture the moment even though you may never see your subjects again.

It is a good idea to ask the adult for permission, but as long as you don’t invade anyone’s privacy, most people don’t mind being photographed and will probably ask for a peek at your LCD or even a print, and you can offer to email a copy to them.